In java, do I always need a Main class?

Question

I know that I'll need a main method, but can that main method be in a different class other than the Main class?

Answer 1

Not all Java applications require a main method:

• Web applications using Servlets and such do not involve a main method.
• In Java 9+, having a main method is optional in JavaFX apps per JEP 153: Launch JavaFX Applications.

The answer to your question depends on what exactly you mean. Do you mean a class with the name Main? Then, no, there is no requirement for this at all.

The only requirement that Java has, is that the signature of the method is correct. The main method must:

• be public
• be main
• be static
• have returntype void
• accept an array of Strings as (only) parameter

It's easier to add it in the public class in a file, but not mandatory. The name of the class it is in, is entirely up to you, though many will choose a name like 'Main' or 'Open', simply to more easily find it.

If you want to be able to run your application, by simple double-clicking the .jar file, you'll need to point to the class that contains the main method (to use: your application might contain a lot of main classes, used for internal testing, but only one can be used to start the actual application) in the manifest file: Manifest files

Prior to Java 7, it was possible to run a desktop application without a main method, by (ab)using an instantiation block, but this was removed as of Java 7, because this is not what the instantiation block was intended for.

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Some of those rules listed above may be relaxed in future versions of Java.

Java 22 previews a feature to greatly simplify declaration of a main method and its containing class. See JEP 463: Implicitly Declared Classes and Instance Main Methods (Second Preview).